Underwater PV research floats US Navy's boat

Pete Danko EARTHTECHLING, 22nd October 2016

The U.S. Navy is trying to figure out ways to create power with underwater photovoltaics, and making some progress.

But an answer to the big question - why? - is one that's a little tough to nail down.

"Underwater autonomous systems and sensor platforms are severely limited by the lack of long endurance power sources," the Navy said, as if that clears things up.

The presumption is this means underwater solar power generation could run some kind of environmental monitoring device, measuring bacteria counts or water temperatures, that kind of thing. But, hey, it's the Navy, so maybe there's more of a James Bond military-spy angle to it.

In any case, the Naval Research Lab in Washington, D.C., said it was progressing on high bandgap solar cells that could produce enough power at 9 meters underwater – around 30 feet – to "operate electronic sensor systems."

The first challenge here is obvious: sunlight traveling through 30 feet of water isn't going to be as powerful as unfiltered sunlight. But the Navy said that if you match the solar cell to the narrow wavelength range, you might be able to eke out adequate power. The Navy researchers used gallium indium phosphide (GainP) cells, which are commonly used in space applications.

No surprise they went in that direction, really; Phillip Jenkins, the man leading the research, told us he worked for years on space-based photovoltaics with NASA.

The Navy said preliminary tests reveal that a square meter of solar cells at that 30-foot depth could produce 7 watts. That's not a lot, but Jenkins pointed out that that increasingly energy-efficient electronics are trimming the power requirements for devices.

Having answered the most basic question of viability, Jenkins said the next task was to work on the underwater PV in the context of whole-system considerations. That includes taking on the the question of how their PV might survive in an environment potentially much more hostile than an open-air placement.